Abstract: A process for treating effluent from a flue-gas desulfurization system wherein the resulting gypsum is removed, comprises filtering the gypsum and fly ash free effluent by a filter, transferring the filtrate to an electrodialyzer wherein cation-exchange membranes and univalent anion-exchange membranes are alternately set up, concentrating chlorine ions in the solution therein by dialysis, further concentrating the solution by evaporation in an evaporator, kneading the concentrated solution with cement or a mixture of cement and coal ash to a solid matter with no harm, and thereafter abandoning for landfill; and an apparatus for treating effluent from a flue-gas desulfurization system, comprising a filter for filtering the effluent to a turbidity low enough for treatment by an electrodialyzer wherein the effluent is to be separated into concentrated and dilute solutions, the electrodialyzer equipped with an alternate arrangement of cation- and anion-exchange membranes, with concentration and dilution compartme